I walked around to The Dolphins Swimming (and Rowing) Club, and used their facilities. They have their own liitle stretch of beach behind the club, so I just walked down the steps and got into the sea from there. The water temperature was 61 degrees Fahrenheit according to their board (16C). It felt like a winter swim in Sydney, but someone that I was talking to told me that this was their top temperature for the Bay.
I swam off in the direction of the Golden Gate Bridge, but within the shelter of the Aquatic Park surrounding piers and marker buoys. I was in the water for about half an hour or so. It was an amazing swim, but I was glad of the hot shower afterwards.